Dislocation-mediated functionality in bulk ferroelectrics
Dislocations are 1D topological defects that exert control over composition, strain, and charge at extended length scales. They offer an additional means to tailor thermal and electrical conductivity beyond the limitations imposed by traditional bulk doping. In contrast to atomistic doping, the dislocation structure is stable to several hundred degree Celsius. In the case of ferroelectrics, dislocations act as nucleation sites for domain formation and serve as pinning centers for the motion of domain walls, which are 2D topological defects. However, the potential of extended dislocations in bulk ferroelectrics has been widely underestimated. Furthermore, uniaxial plastic deformation can induce irreversible and elastic strain fields in ferroelectrics, allowing for the permanent tailoring of elastic energy. This means that dislocations possess the capability to impart strain modifications to bulk ferroelectrics.
In this talk, my focus will be on a novel approach to manipulate the mobility of ferroelectric domain walls and piezoelectricity of single-crystal BaTiO3. Specifically, we achieved a 19-fold increase in the converse piezoelectric coefficient by imprinting dislocations via high-temperature creep along the  direction. By employing controlled high-temperature plastic deformation along the  direction, we successfully optimized the dielectric and electromechanical properties of the material. This optimization was achieved by leveraging the anisotropic interactions between 1D dislocations and 2D domain walls. Time permitting, we will discuss the domain instability and extrinsic degradation processes that can both be mitigated during the aging and fatigue with a careful strain tuning of the ratio of in-plane and out-of-plane domain variants. Intrinsic strain engineering in bulk ferroelectrics highlights the potential of plastic deformation as a means to tailor the microstructure and functionality of ferroelectrics. Texture will be quantified using nuclear paramagnetic resonance (Dr. Pedro Grosczewicz) and temperature dependent domain evolution will be revealed using in-situ transmission electron microscopy (group of Xiaoli Tan). If accessible, I may report on options to introduce dislocations into polycrystalline oxides in general and ferroelectrics specifically.
卓芳平博士， 2018年获乐鱼足球理学博士学位，2017年在瑞士洛桑联邦理工学院Dragan Damjanovic教授课题组访学，2019年至2020年在韩国科学技术研究所(KAIST)物理系Chan-Ho Yang教授课题组担任博士后研究员，2020年至今在德国达姆斯塔特工业大学材料和地球科学系Jürgen R?del教授课题组从事研究工作。主要研究兴趣包括铁性材料的缺陷工程和基于机器学习的压电力显微镜技术。主持德国洪堡博士后基金、达姆施塔特工业大学种子基金和德国自然科学基金(Deutsche Forschungsgemeinschaft， DFG)各一项。